1. Field of the Invention
The present invention relates to a display device and a method for driving the same, and more particularly to a spontaneous light emission type display device with pixels having a high aperture ratio and a method for driving the display device.
2. Description of the Related Art
Of late, organic electroluminescent display devices have received attention as flat-panel electroluminescent display devices having a large viewing angle. Some organic electroluminescent dot-matrix display devices are active-matrix drive type, and others are simple-matrix drive type.
A conventional organic electroluminescent display device 350 is active-matrix drive type, and has organic electroluminescent elements 351, a plurality of drive transistors 352 for applying voltages to the electroluminescent elements 351, a plurality of capacitors 353 for retaining the applied voltages, and a plurality of selection transistors 354 for selectively writing image signals into the capacitors 353, as illustrated in FIG. 17 which is a diagram showing an equivalent circuit (corresponding to one pixel). The gates of the selection transistors 354 are connected to a gate driver via gate lines GL, while the drains of the selection transistors 354 are connected to a drain driver via drain lines DL.
When driving the organic electroluminescent elements 351, the selection transistors 354 are selected line by line in accordance with selection signals supplied from the gate driver. The drain driver writes image signals into the capacitors 353 in a currently selected line through the drain lines DL and the selection transistors 354. The drive transistors 352 drive the organic electroluminescent elements 351 in accordance with the magnitudes of the image signals written into the capacitors 353. Voltages according to gradations are applied to the organic electroluminescent elements 351, thereby making the display device display desired images. Thus, in the case of the organic electroluminescent display device 350, the selection transistors 354 are selected line by line, in which case there is no possibility of an unintended voltage being applied to the organic electroluminescent elements 351 in lines other than the currently selected line. This enables the display device to display images without the crosstalk occurring.
According to the organic electroluminescent display device 350 of the active-matrix drive type, however, the drive transistors 352, the capacitors 353 and the selection transistors 354 have to be formed in addition to the organic electroluminescent element 351 constituting each pixel. This entails a problem in that the area (aperture ratio) of the organic electroluminescent element 351 forming each pixel is small.
As shown in FIG. 18, an organic electroluminescent display device of the simple-matrix drive type includes a substrate 360, anode electrodes 361, an organic electroluminescent layer 362 and cathode electrodes 363, which are all laminated on the substrate 360. The anode electrodes 361 are perpendicular to the cathode electrodes 363. The intersections of the anode electrodes 361 and the cathode electrodes 363 are pixels. In the organic electroluminescent display device of the simple-matrix drive type, the aperture ratio of the pixels is higher than the aforementioned case.
According to the organic electroluminescent display device of the simple-matrix drive type, however, there is the possibility of a voltage being applied also to those parts of the organic electroluminescent layer 362 which are located on the anode electrodes 361 of the pixels in lines other than the currently selected line. Thus, when an unintended voltage is applied, crosstalk occurs due to the voltage-luminance characteristic of the organic electroluminescent layer 362, resulting in a low contrast ratio.